1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a head suspension assembly to a head actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or "gram load". Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load. A spring section of the load beam is formed to provide the load force that counteracts the aerodynamic lift force generated by the rotating disk during operation of the disk drive.
A head-carrying suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. The combined base plate, load beam and a flexure make up a head suspension, and the suspension typically has the hub of the base plate extending through and beyond the load beam clearance hole.
The hubs of two suspensions are inserted into an actuator arm boss hole formed through an actuator arm extending from an actuator body, one hub entering an actuator arm boss hole from each end of the hole. A swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss hole. Thus, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
A typical base plate has two primary regions, a flange region and a hub region. The flange region is a flat portion to which the load beam is welded. This area preferably remains flat and free from distortion so that it serves as a stable mounting feature for the load beam and ideally remains so throughout the swaging operation. Extended base plates are known in the art. One reason to extend a base plate flange beyond the arm clamping region is to get better clamping conditions by moving the weld points beyond the clamping area. This provides a clean mounting surface where the base plate flange meets the actuator arm mounting surface. A second advantage is that the stacking height is reduced or alternatively a thicker base plate is possible while maintaining the same stacking height.
The hub region is an extended boss whose upper end is contiguous with the flange portion and whose lower end passes through boss clearance holes in both the load beam and the actuator arm. The hub region supplies the retention torque between the base plate, which is welded to the load beam, and the actuator arm by plastically expanding and cold working during the swaging operation, creating a press fit with the actuator arm. A problem with this process is that the base plate flange becomes warped by stress from the hub during the swaging operation. Consequently, the load beam, which is welded to the base plate flange, is deformed by the warping of the base plate flange, adversely affecting the gram load on the transducer head. After assembly, the gram load is tested and if not correct the spring section of the load beam is bent appropriately to adjust the gram load to a predetermined standard. This operation may further distort the load beam and adversely affect the dynamic performance thereof.
It is, therefore, desirable to provide an actuator arm assembly for a magnetic disk unit in which a base plate provides an extended flange region to provide a strain concentrated region about which there is an axis of bending to provide gram load adjustment while also absorbing stress occurring during a swaging operation so that the base plate and a load beam welded thereto will not be excessively warped as a result of swaging. Additionally it is beneficial if such a strain concentration region were manufactured with a pre-formed bend to eliminate the need for costly bending of the resilient load beam during suspension assembly manufacturing.